The present invention relates to the positioning of an additional tubular element on a tubular structure which may be subject to a random movement and where the planes of the end surfaces of the structure and of the additional element to be brought into contact have slight angular deviations with reference to each other and with reference to the corresponding theoretical planes orthogonal to the respective longitudinal axes of the structure and the additional element.
Since the aim is to make the two confronting end surfaces coincide, there are two difficulties due to the particular conditions involved.
With regard to the angular deviations mentioned, it will be understood that they may constitute the major obstacle to correct positioning, i.e. to realising simultaneously the coincidence of the end surfaces and the alignment of the axis of the additional element with that of the original structure.
The problems produced by angular deviations in the end surfaces can, in certain cases, be overcome, where the ends of the element and of the structure are to be welded together, after positioning. If the welding process adopted is welding by high-frequency electric current and if the additional element is applied to the structure with a high compressive force, this has the effect of causing upsetting of the material, as occurs during forging, so as to bring the two end surfaces into coincidence, respecting as far as possible the coaxiality of the additional element relative to the structure. Such a method may also be applied even in cases where strict coaxiality of the element and the structure is not essential. It will be appreciated that whatever the welding process adopted, and more particularly where electron beam welding is involved, the primordial condition for good assembly remains the realisation of perfect coincidence between the end surfaces in contact. This is also so in the case of assembly by screwing.
With the regard to the movements to which the original structure may be subject, they are likewise such as to compromise the success of the assembly operation, without considering the damage which might result to the components involved. From this point of view, it is necessary to ensure good retention of the element relative to the structure to enable risks associated with relative random movement to be avoided.